An acid-free route for the facile synthesis of iron-functionalized mesoporous silicas: Transformation between hollow nanospheres and cage-like mesostructures

Abstract

a b s t r a c tIron-substituted silicas with hollow nanospherical morphology and cage-like mesostructure have been synthesized using triblock copolymer F127 as surfactant and tetramethoxysilane (TMOS) as silica source with no necessary addition of mineral acids. Iron-functionalized hollow nanospheres were obtained using Fe(acac) 3 as iron source. When Fe(NO 3 ) 3 was employed as iron source, iron-containing cage-like FDU-12 mesostructure and hollow nanospheres were formed with Fe/Si molar ratio lower than 0.008 and higher than 0.015, respectively. The formation of hollow spheres at high Fe/Si ratio can be regarded as gradually dissociation of nanocages from Fe-FDU-12. The structure of the iron centers was determined by spectroscopic methods (UV-vis and UV-Raman measurements) and by elemental analyses. The facile structural evolution between cage-like and nanospherical structures may be helpful for further understanding the formation mechanism of mesoporous silicas.

Oriented Decoration in Metal-Functionalized Ordered Mesoporous Silicas and Their Catalytic Applications in the Oxidation of Aromatic Compounds

“…In this case, the hollow mesoporous silica spheres should be focused on due to their regular morphology, low density, and short diffusion path which permits the convenient diffusion of reactant molecules in and out of the hollow spheres [94][95][96]. Owing to this hollow spherical morphology, the metal-functionalized OMSs catalysts exhibit superior catalytic performances [19,97,98]. The reactant molecules can diffuse through the silica shell to reach the interior of hollow sphere, and thus the frequency of the contact with active metals from both outside and inside is significantly improved, leading to the acceleration of catalytic reaction.…”

“…This direct synthetic pathway provides more advantages in metal-functionalized OMSs, such as short preparation time, the homogeneous distribution of organometallic complexes, increased metal loading amount, suitable pore size and pore arrangement. Furthermore, due to the mismatch for the incorporation of transition metal ions and the formation of silica, the control of morphology and structure of OMSs would be more difficult [18,19]. For example, nonionic surfactants (such as P123 and F127) have been widely used as templates for the fabrication of HMS (Hexagonal Mesoporous Silica), normally in strongly acidic conditions [20].…”

Heteropoly acid and ZrO2 bifunctionalized organosilica hollow nanospheres for esterification and transesterification

“…[11][12][13] Generally, various active species could be incorporated into both the hollow interior and the shell of silica, organosilica or carbon hollow nanospheres, however, compared with the preparation of pure silica, organosilica or carbon hollow nanospheres, the fabrication of silica-, organosilica-or carbon-based hollow nanosphere composites/hybrids functionalized by various catalytically active components via a one-pot route rather than the postsynthesis graing method is more difficult, and only a limited number of research papers are concerned about this topic. [14][15][16] Therefore, the preparation route should be designed carefully to ensure the structural integrity of the functionalities and perfect hollow nanospherical morphology with controllable particle size. The general approaches for the fabrication of hollow nanosphere composites/hybrids include so/hard template and self-templating methods depending on the nature of the template.…”